1. Technical Field
This invention relates to digital image display systems and, more particularly, to a terminal independent color memory for such systems.
2. Description of the Prior Art
Methods and apparatus for providing color digital images on video display screens are well known. A problem, however, has arisen in that compatability among digital display systems has been made difficult by the great variety of methods and apparatus for providing the color images. For example, the Picture Description Instructions PDI for the Telidon Videotex System, CRC Technical Note No. 696-E, developed by the Canadian Department of Communications describes a specific color value selection method: a direct selection of data values for the primary colors--red, green and blue. The Prestel videotex customer terminal developed by the British Post Office and the Antiope terminal developed by the French CCETT employ a technique for specifying both a foreground and a background color by indexing a permanent read-only color memory.
In the art of color computer graphics, the terminal manufacturers generally employ a color look-up table called a color map indexed by a binary number. The application of a color map expands the repertory of available colors for display. In particular, the Tektronix 4027 terminal is capable of providing 8 colors for direct use from the 64 possible color values that may be loaded into its color map. Other features such as blinking may be provided by such terminals; however, the various methods and apparatus for providing such features are similarly incompatible.
With the advent of videotex, also known as viewdata, and teletext services wherein a customer is able to access a remote host computer and associated data base with a digital image display terminal, there has arisen a need to solve the above-described problems from employing incompatible terminals. There remains a requirement for a terminal-independent color memory for a digital image display system.